This application incorporates by reference of Taiwan application Serial No. 090126957, filed Oct. 30, 2001.
1. Field of the Invention
The invention relates in general to a composition of an ink-jet ink, and more particularly to an ink-jet ink containing glycol compounds with grafts, for providing the printing media with high printing quality.
2. Description of the Related Art
The Ink-jet printing technology is well developed and has the advantages of low cost, low noise, and being capable of providing full-color prints with ease. Furthermore, a high-quality printed image can be produced not only on specialty recording media, but also on inexpensive plain papers and transparency films.
Ink-jet inks can be generally classified as dye inks or pigment inks by the colorants therein. Compared with pigment inks, dye inks have higher water solubility, and provide brighter colors but with inferior light fastness and water fastness. Two common additives for improving the water fastness of the dye inks are organic compounds and resin, which enhance the adhesive force between the colorant and printing medium. On the other hand, pigment inks provide less bright colors and tend to cause the clogging of the nozzle due to the large particle size. Thus, dispersing pigment inks are desired.
Freedom from feathering in the printed image is one of the key requirements of the ink-jet ink. Ink-jet inks with low cohesive force could result in feathering by the aid of the capillary of the paper. A surfactant is therefore usually added to adjust the surface tension and viscosity of the ink and to ensure the image quality.
Another key requirement of ink-jet inks is high drying speed. However, the ink-jet ink is hard to dry since it is usually water-based. Enhancing the penetration of the ink could result in high drying speed of the ink, and adding an agent with high volatility is an alternative method. However, ink added with high-volatility agents could form a crust over the tip of an ink-jet nozzle, which would stop the printer from working properly. In general, dye inks have higher penetration and dry within 1 second, and pigment inks have lower penetration and take longer than 10 seconds to dry.
In short, pigment inks have superior water fastness and light fastness, but are hard to dry. Thus, increasing the drying speed of pigment inks is an important issue.
It is therefore an object of the invention to provide an ink-jet ink, which has low surface tension and high drying speed. It is a further object of the invention to provide an ink-jet ink, which has high adhesive force between the ink drops and the printing medium, thus providing the printing medium with high water fastness.
The ink-jet ink of the invention comprises a medium, a colorant, and a glycol compound with grafts, wherein the colorant is a dispersing pigment, the medium further comprises an aqueous solution, and the glycol compound with grafts is water-soluble. The glycol compound with grafts can be one or any mixture of the following: 2-ethyl-1,3-hexanediol; 2,4-diethyl-1,5-pentanediol; 2-butyl-2-ethyl-1,3-propanediol; 2,2-dimethylpropane-1,3-diol; and 2,5-dimethylhexane-2,5-diol. The glycol compound with grafts in the ink-jet ink is about 0.01 wt % to 25 wt %, and the number of grafts of the glycol compound is between 4 and 20. The average particle size of the pigment is less than 1 xcexcm. The medium could further comprise a surfactant, an organic solvent, a humectant, a pH buffer, and a biocide.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.